drm/i915/gvt: make mmio_context.h self-contained

Add necessary #includes and forward declarations to make the header
compile on its own.
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/979ba0ea394e9589f7332b94e91ac200faf995c5.1607422863.git.jani.nikula@intel.com

drivers/gpu/drm/i915/Makefile

@@ -285,7 +285,6 @@ obj-$(CONFIG_DRM_I915_GVT_KVMGT) += gvt/kvmgt.o
 no-header-test := \
 	display/intel_vbt_defs.h \
 	gvt/gvt.h \
-	gvt/mmio_context.h \
 	gvt/mpt.h \
 	gvt/scheduler.h
 

drivers/gpu/drm/i915/gvt/mmio_context.h

@@ -36,6 +36,17 @@
 #ifndef __GVT_RENDER_H__
 #define __GVT_RENDER_H__
 
+#include <linux/types.h>
+
+#include "gt/intel_engine_types.h"
+#include "i915_reg.h"
+
+struct i915_request;
+struct intel_context;
+struct intel_engine_cs;
+struct intel_gvt;
+struct intel_vgpu;
+
 struct engine_mmio {
 	enum intel_engine_id id;
 	i915_reg_t reg;